Ch. 24 The Operon (Final Exam)

Question 1

This term refers to the functioning unit of DNA consisting of clusters of genes under the control of a single promoter.

Answer 1

Operon

Question 2

What is the relationship between genes included in the operon?

Answer 2

These genes code for proteins with related functions

Question 3

Are you more likely to find the operon in prokaryotes or eukaryotes?

Answer 3

Prokaryotes

Question 4

What are the 3 basic components of an operon (HINT: POS)?

Answer 4

1) Promoter
2) Operator
3) Structural genes

Question 5

This site is the nucleotide sequence recognized by RNA polymerase that enables gene transcription.

Answer 5

Promoter

Question 6

What is an operator?

Answer 6

Segment of DNA that a repressor binds to

Question 7

These genes are co-regulated by the operon.

Answer 7

Structural genes

Question 8

These are constantly expressed gene that codes for repressor proteins.

Answer 8

Regulatory genes

Question 9

These proteins suppress gene transcription in response to external stimuli.

Answer 9

Repressors

Question 10

Proteins that increase gene transcription in response to external stimuli.

Answer 10

Activators

Question 11

Small molecular structures that displace the repressor from the operator site to activate the operon.

Answer 11

Inducers

Question 12

Protein that helps a repressor bind to the operator site by binding to the repressor itself

Answer 12

Corepressor

Question 13

This type of operon involves a repressor bound to the operon that normally prevents transcription in this instance, so an inducer binds to that repressor to allow for transcription.

Answer 13

Negative inducible operon

Question 14

Why does an inducer binding to a repressor enable transcription?

Answer 14

Structure determines function, so the inducer binding to the repressor alters the structure of the repressor, which totally changes its function

Question 15

During transcription, this operon involves a corepressor that binds to a functionally inactive repressor so it can bind to the operon and stop transcription

Answer 15

Negative repressible operon

Question 16

This operon involves activator proteins that are normally unable to bind to DNA and start transcription on their own in this instance, so an inducer binds to the activator and allows transcription to start.

Answer 16

Positive inducible operon

Question 17

This operon involves activator proteins that are bound to the DNA and transcription is happening, a corepressor binds to the activator and stops transcription.

Answer 17

Positive repressible operon

Question 18

SHORTCUT/TIP: Positive refers to…

Answer 18

An activator being bound to something

Question 19

SHORTCUT/TIP: Negative refers to…

Answer 19

A repressor being bound to something

Question 20

SHORTCUT/TIP: Repressible refers to…

Answer 20

Stopping (repressing) transcription

Question 21

SHORTCUT/TIP: Inducible refers to…

Answer 21

Starting (inducing) transcription

Question 22

Why is the lac operon negative inducible (HINT: describe its function in 2 steps)?

Answer 22

1) A repressor is bound to the operator, thus inhibiting transcription
2) An inducer then binds to the repressor, which deactivates the repressor and allows for transcription, in the presence of lactose

Question 23

The E. coli lac operon has a second layer of control called catabolite repression. What is the basis of this concept?

Answer 23

The lac operon cannot be turned on by lactose if there is a sufficient supply of glucose, as glucose is the better energy source

Question 24

In catabolite repression of the lac operon, what is the name of the protein complex that serves as a positive regulator to induce transcription?

Answer 24

cAMP-CAP protein complex

Question 25

How does the cAMP-CAP complex work?

Answer 25

Cyclic AMP (cAMP), an inducer, binds to catabolite activator protein (CAP), an activator, to assist the RNA polymerase in initiating transcription

Question 26

What happens to cAMP levels when glucose levels drop, and what is this relationship called?

Answer 26

When glucose levels drop, cAMP levels increase. The levels of these molecules are inversely proportional

Question 27

How does the tryptophan (trp) operon operate on negative repression?

Answer 27

Corepressors bind to an inactive repressor to activate it, and this repressor stops transcription in the presence of tryptophan

Question 28

Why is the tryptophan operon important to E. coli?

Answer 28

E. coli need amino acids like tryptophan to survive, so the trp operon is transcriptionally active and synthesizes tryptophan when there is none present